Physicians require blood tests for a variety of reasons and current technology allows a physician to learn much about a patient's condition by testing blood alone. One standard sampling procedure for blood involves the use of a pre-evacuated test tube and a cannula with two penetrating ends. In order to obtain a blood sample, one end of the cannula is inserted into the donor's vein and the opposite end of the cannula is inserted through a rubber cap which makes an air tight seal on the end of an evacuated tube. The pre-evacuated tubes are sealed with a cap or plug which makes an air tight seal and maintains negative pressure in the tube. One such commercially available tube is manufactured by Becton Dickenson, of Rutherford, N.J. and sold under the trademark VACUTAINER. Some tubes are sold with gels or other filter means which are designed to be inserted in a centrifuge to separate various components in blood. The tubes have a round bottom and are made or either glass or plastic with a silicone rubber stopper. The stopper is typically constructed of isobutylene-isoprene rubber or chlorinated isobutylene-isoprene rubber. The stoppers are inserted in the tubes very tightly to prevent spillage and the loss of pressure during shipment. Negative pressure maintained in the tube facilitates the transfer of blood from the donor to the test tube. Intravenous blood pressure of the patient also provides assistance to flow blood from the vein to the test tube and, in fact, intravenous blood pressure can create positive pressure in the sampling tube after the sampling procedure is completed. After the sample is retrieved, the needle is withdrawn from the rubber stopper and is suitably disposed. The rubber stopper collapses and re-seals itself to maintain an air-tight condition. The sampling tube serves as a convenient and safe storage receptacle for the sample which can be sent to laboratories in remote locations from the sampling location for analysis.
After the sampling procedure, a barrage of tests may be performed on the blood sample each of which require a portion of the fluid from the sample. In hematology, whole blood samples are used. A number of other clinical chemical blood analyses require the separation of various components from whole blood before testing because the components may interfere with the administration of the analyses. For example, many analyses require the separation of cellular components and the fibrin from the blood before testing. Separation procedures, which can involve filtration or centrifugation and combinations thereof, are often performed in the evacuated sample tube. The primary difference between serum and plasma is their content of fibrinogen which is in large part removed by the clotting process. Fibrinogen, which is present in blood plasma, is converted to fibrin during clotting of blood. Regardless of the test procedure used, when whole blood, blood serum or blood plasma is tested, a portion of the liquid must be removed from the evacuated sample tube and transferred to the testing apparatus. Consequently, a number of methods and apparatus for this procedure have been developed which attempt to balance competing considerations of safety, convenience, and expense. The transfer should be able to be effected quickly with low cost while maintaining a safe environment for the blood technicians. Blood may contain biologically hazardous components which can expose laboratory technicians to the risk of contracting contagious disease. Accordingly, the potential for exposure to the blood should be minimized. Furthermore, it is important to ensure the blood or fluid is not contaminated during the transfer procedure which could lead to inaccurate testing results.
Present sampling procedures employ a number of different methods to effect this type of transfer however each transfer method has a number of disadvantages and limitations. For example, one current procedure for the sampling of blood components from evacuated tubes involves the removal of the cap or plug from the sample tube and then either pouring the sample from the tube or using a transfer device such as a pipette. The removal of the cap however presents an unnecessary risk of exposure. The blood could be spilled or released into the air by an aerosol effect. Due to engineering constraints, removal of the cap places high stress on a test tube which could fracture the tube thereby presenting another avenue of exposure. The cap forms a tight seal with the tube to maintain an air tight condition and, accordingly, the manual manipulation of the cap is difficult. More importantly, the removal of the cap can cause a dangerous aerosol effect, especially when the pressure within the sample tube is different from the air pressure in the environment. When the tube is under positive pressure the aerosol effect is exacerbated because air rushing out of the tube can propel small drops into the air. When the cap is removed from the tube, it is often placed upon the technician's working surface which can then contaminate the working surface and present a further risk to the technician. Contamination of the working surface also presents the risk of contamination of the remainder of the sample under analysis from blood which has escaped from previously tested samples and is present on the technicians' working surface.
After removal of the cap, the blood must be transferred by suitable means to the testing apparatus. Preferably the transfer device should be disposable to avoid the problems and expense associated with cleaning the device after use. Furthermore the transfer device should be easy to manipulate, minimize exposure of laboratory technicians and be capable of quick and easy operation. Pipettes, which can be constructed of glass or plastic, are routinely used to obtain blood or serum samples either directly from evacuated tubes or from open storage receptacles. Pipettes however have a number of disadvantages for the instant application. Although pipettes are effective at transferring small precise volumes of fluid to precise locations, pipettes are also not well suited to transfer larger amounts of liquid from a sample test tube because they have no fluid reservoir. Use of pipettes would take an unreasonable amount of time to transfer larger volumes of fluid from a sample tube to another location. Pipettes must be provided with a means for suction to draw the liquid into the narrow tube. One common device is a resilient bulb which is constructed of rubber and intended to be reused. These bulbs are relatively expensive and somewhat difficult to manipulate because they must be changed from each pipette. Furthermore the bulbs require cleaning in the event blood is drawn into the structure.
There are disposable pipettes commercially available which have an integral resilient bulb designed to draw fluid into the pipette. The bulb can serve as a fluid reservoir, but the device is not generally designed to quickly transfer larger amounts of fluid.
A further drawback associated with the use of pipettes relates to the risk of contamination. Since sampling requires immersion of the end of the pipette in blood, the outer surfaces of the pipette are covered with blood. Although the pipettes are disposable, this exposed surface presents the possibility of the blood dripping off on to the technician or the working surfaces.
Recapping the tubes also presents yet another opportunity for spillage and exposure from contact with the stopper which is often contaminated with blood.
One method to obtain a blood sample while avoiding the removal of the cap is to penetrate the cap with the transfer device. Commercially available pipettes are not strong and durable enough to penetrate the standard rubber cap on an evacuated tube or designed for such penetration. For example, the diameter of disposable transfer pipettes which were previously described and are currently on the market is typically 0.130 inches with a 0.090 inch diameter fluid passageway. Pipettes with such dimensions will not puncture the rubber cap on an evacuated tube without considerable effort. Even if such pipettes were strong enough to puncture a rubber cap without breaking, they are not well designed for this purpose because there is no flange structure to adequately hold the pipette and allow the application of sufficient force to puncture a rubber cap or plug. Furthermore the ends of pipettes are not sharpened to a point which would help enable the pipette to penetrate a cap.
Conventional micro pipette assemblies which include a holder, a pipette and an overflow chamber are likewise not well suited for this application. There are a number of ancillary devices sold in association with pipettes for the specific purpose of puncturing diaphragms on reservoirs containing diluents and other types of medicants, however these devices are not designed to puncture the relatively thick caps employed with pre-evacuated tubes.
One device which avoids removal of the rubber cap in blood sampling recognized the problems associated with current procedure and disclosed using a punch to puncture the stopper on such standard evacuated tubes and draw the sample through the hole made in the stopper made by the punch. It is apparent that the developer considered the problems with designing a punch which would allow a technician to exert sufficient amount of force on the punch to penetrate the rubber cap because the device included a cowling or shroud for alignment purposes and contemplated the use of a mechanical press mechanism in order to puncture the rubber stopper. After insertion into the rubber stopper, the punch is apparently intended to remain in the sample tube. The size of the punch disclosed apparently results in an opening too large to be resealed by the collapse of the stopper. Inserted within the punch is a pipette which has a resilient reservoir for sampling the liquid in the sample test tube. One embodiment does not provide an air tight seal between the interior walls of the punch and the exterior walls of the pipette and as such the system can only be used in an upright position. This arrangement is not desirable because the remaining sample is exposed to the air and presents the problems associated with spillage or the opening must be sealed with a second cap. The central passage of the punch disclosed in the prior art must be able to receive a typical transfer pipette which has an outer diameter of approximately 0.130 inches. A punch made this size would be too large to manually penetrate a typical rubber stopper without considerable effort. Punches which have large diameters exert greater stress on the sample tube which increases the risk of accidental fracture of the tube and the potential for coring of the stopper.
Some of these limitations were recognized and another embodiment was proposed with a second cap designed to fit in the hole formed by the punch. Within the second cap is a diaphragm comprised of polyurethane foam. The diaphragm has a vertical cut specifically designed to be able to be penetrated by a sampling pipette.
Metal needles or punches are commonly used to penetrate rubber stoppers such as those found on bottles which contain medicine or drugs and from evacuated tubes; however, the use of metal is undesirable because of the risk of accidental puncture injury. Currently the use and disposal of "sharps" is subject to a number of regulations because of the risk of accidental contamination and needle sticks. Furthermore, smaller needles would take an unreasonable amount of time and would not provide an expedient means for the transfer because of the small diameter of the passageway. Metal needles or punches also present problems associated with the attachment of the needle to the receptacle. Accordingly, the use of metal components is best avoided.